Arc furnace electrode control apparatus



J. W. MOORE ARC FURNACE ELECTRODE CONTROL APPARATUS Jan. 24, 1967 FiledJan. 15, 1964 INVENTOR 77765 Z/ry/rt M70076 Jan. 24, 1967 w, MOQRE ARCFURNACE ELECTRODE CONTROL APPARATUS 5 Sheets-Sheet 2 Filed Jan. 13, 1964A/E/I/Vl/E/V INVENTOR i 77785 Zfight Mame 5 M wfttormy iiii -uHIunu illJan. 24, 1967 J. w. MOORE ARC FURNACE ELECTRODE CONTROL APPARATUS 3Sheets-Sheet '5 Filed Jan. 13, 1964 INVENTOR. ames Mfg/2t ukao/"e m wkFR m m & NM Q United States P ent O" I 3,300,562 ARC FURNACE ELECTRODECONTROL APPARATUS James W. Moore, Pittsburgh, Pa., assiguor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware I Filed Jan.13, 1964, S81. No. 337,289

' 13 Claims. (Cl.13-;13) I This invention relates toelectric arcfurnaces and more particularly to apparatus for controlling the positionof arc furnace electrodes.- 1 -It iscommon practice in the production ofhigh-grade steel to utilize polyphase electric arc furnaces having aplurality of electrodes and electrode positioning means as-sociated witheach electrode. Current flow in such furnacesis from the electrodes tothe grounded furnace charge. That portion of the current path'betweenthe electrodes and the. furnace charge is an are which provides the heatnecessaryfor furnaceoperation.

Means are gene-rally provided toposition each of the electrodes relativeto thefurnace charge in accordance with the length of its respective arcas indicated by the arc current and the arc voltage so that when the arccurrent rises, indicating that the arc is too short, the electrode israised, and when the arcvoltage rises, indicating that the arc is ,toolong,.the electrode is lowered.

One type of electrode positioning apparatus employs a: reversiblehydraulic motor which is connected to the electrodes by means of anelectrode clamp and a positioning arm. The hydraulic motor is connectedto a source of hydraulic pressure through a hydraulic control mechanismwhich couples the ram to the source of hydraulic pressure inaccordancewith the electrical conditions'in the furnace. Such hydrauliccontrol systems generally include a servo valve which metersthe flow ofhydraulic fluid between the hydraulic ram and the pressure source inaccordance with electrode current, and 'voltage conditions. In order toachieve sufllcient amplification for the operation of the servo valve,it was often necessary to employ a'pilot valve and an intermediatecontrol valve between the voltage and current sensing portions of the'device and the servo valve.' There is a tendency foreach valve in theamplification stages to slightly overshoot and this is multiplied byeach succeeding stage so that such controlisystems have a tendency tohunt. Various schemes have been tried to compensate for such hunting butthese tend to make control apparatus complicated and costly. Thishunting is due to a phenomenon known as orificereaction, that is,thetendency for hydraulic fluid acting on a piston-type valve when thevalve port is first opened to move the valve element beyond its desiredposition.

It is'an object of the invention to provide control apparatus for thehydraulic positioning assembly of an arc furnace electrodewhereinmetering of the hydraulic fluid is accomplished by pinch valves whicharefree from orifice reaction'disturbances.

' Another object of theinvention'is'to provide a control means for thehydraulic positioning assembly of an arc furnace electrode whereinhydraulic metering is controlled by an electromagnetic variabletransmission device to eliminate the necessity for hydraulic sensing andamplifying elements. v

A further object of the'invention is to-provide a control apparatusfo'rthe hydraulic positioning assembly of an arc furnace electrodewhereinelectromagnetic clutch means energized in'accordance withelectrical conditions in the are for coupling continuously running'motormeans to valve means so that the electrode is lowered when" its voltageexceeds a preselected value and raised when its current exceeds apreselected value. An object of one embodiment of the invention is toprovide such apparatus with biasing means coupled to said clutch in amanner tending to operate said valve means in an electrode loweringdirection and wherein an electrical signal is applied to said clutchmeans in an opposing sense relative to said biasing means. An object ofanother embodiment of the invention is to provide such apparatus withfirst and second electromagnetic clutches respectively energizable bysignals proportional to voltageand current and each acting in oppositionon reversible valve operating means.

These and other objects and advantages of the instant invention willbecome more apparent from the detailed description thereof taken withthe accompanying draw ings in which:

l FIG. 1 schematically illustrates one embodiment of the electrodepositioning assembly according to the instant invention;

FIGS. 2 and 3 illustrate in greater detail the pinch valve employed withthe control mechanism of FIG. 1; and

FIG. 4 schematically illustrates an alternate embodiment of the instantinvention. 7

Referring now to the drawing in greater detail, an electric arc furnace10 is shown in FIG. 1 to include a furnace body 11 containing a quantityof molten furnace charge or melt 12 and three movable electrodes 13, 14and 15'positioned above the melt 12. The electrodes 13, 14' and 15 areconnected to three-phase supply conductors 16, 17 and 18 respectively,which are, in turn, connected to a suitable source of three-phase power(not shown). A hydraulic motor 20 is mechanically connected to each ofthe electrodes 13, 14 and 15 by an electrode positioning arm 21 so thatsaid electrodes may be raised and lowered in accordance with furnaceconditions. Since identical operating mechanisms are provided forcontrolling the positioning of each of the electrodes 13, 14 and 15,only one is illustrated for the sake of brevity.

The hydraulic motor 20 includes a cylinder 23 and a piston 24 coupled tothe arm 21 and actuated by the control'mechanism according to theinstant invention which is shown to' include a source of hydraulicpressure 25, a hydraulic control assembly 26 connected between thepressure source 25 and the fluid motor 20, and an electrodecondition-sensing circuit 27 for initiating the operation of the controlmechanism 26.

The source of hydraulic pressure 25 includes a hydraulic accumulator 30which is connected by a pump 32 to a fluid reservior or sump 34. In amanner well-known in the art, a motor 36 drives the pump 32 so thatsubstantially uniform high pressure is-maintained Within the accumulator30.

The hydraulic control circuit 26 regulates the flow of hydraulic fluidbetween the fluid motor 20, the accumulator 30 and the sump 34. Control26 includes a first pinch valve 40 which is disposed in a conduit 41connecting the accumulator 30 to the pressure side of the piston 24 anda second pinch valve 42 which is connected in a conduit 44 between thesump 34 and the pressure side of cylinder 24.

FIGS. 2 and 3 show the pinch valve 42 in greater detail to include agenerally tubular body portion 45 having a flange 46 suitably mounted ateach end so that the valve 42 may be connected into the conduit 44. Thetubular body portion 45 has a reduced central portion 48 provided withan opening 50 formed in one side thereof so that one edge of a pinchlever 52 may bear against a flexible lining 53 disposed within thetubular member 45. The lining 53 is suitably aflixed within tubularmember 45 and is formed of any suitable material such as rubber. Thepinch lever 52 is generally L-shaped and is pivotally mounted at one endabout a fixed pin 55. A spring 56 urges clockwise rotation of lever 52,as viewed in FIG. 3, and toward a stop 58. This tends to move the edgeof pinch lever 52 toward the right as viewed in FIG. 2 to force theopposite sides of the flexible lining 53 together and prevent the flowof fluid in conduit 44.

As seen in FIG. 1, valve 40 is identical with valve'42 except that itspinch lever 52a is urged toward counterclockwise rotation to close itsflexible lining by the action of its spring 56a. .In addition, one endof anL- shaped lever 59 and 59a is respectively connected tothe upperend of pinch levers 52 and 52a and both extend in substantial alignmenttoward a valve operating member 71 whose purpose will be discussed ingreater detail hereinbelow.

Valves61 and 64 are provided in the conduits 41-and 44 respectively inorder to isolate the fluid motor 20 from the hydraulic accumulator 30and the sump 34 if so desired. 1

The hydraulic control 26 includes 'adrive motor 70 which is mechanicallycoupled to a disc-shaped valve control member 71 through anelectromagnetic clutch 72. The motor 70 rotates continuously in onedirection to provide a counterclockwise torque'on the valve operatingmember 71 in opposition to a spring 75 and the magni-' tude' of thistorque will depend upon the degree of coupling provided by theelectromagnetic clutch 72.

More specifically, the clutch 72 includes an input member 76 which isrigidly afiixedto the motor'70 output shaft and is rotatable therewith.The clutchinput member 76 is ferro-magnetic and has a cup-shaped recess77 in which a disc-shaped ferro magnetic clutch output member 78 isdisposed. An annular coil 79 is disposed concentrically around the outersurface of the cup-shaped portion 77 of the clutch inputmember 76. Aswill be understood by those skilled in the art, the torque exerted bythe clutch output member 78, and hence. that of the valve control member71, will depend upon the degree of excitation in the coil 79.

-An output shaft 66 is' rigidly aflixed'to' the clutch out-. put member78 and extends upwardly therefrom where its upper 'end rigidly engagesthe valve control member 71. A pair of lugs 67 and 67a extend upwardlyin spaced relation from the upper surface of the valve control member 71and each is disposed adjacent to and spaced from the-free ends of thelinks 59and159a, respectively} It can be seen that when the clutch 72 isin its neutral position shown in FIG. 1, that is, when the torque'onoutput member 78 just balances therestoring force of spring 75 the lugs67 and 67a will be out of engagement with the ends of links 59 and 59aso that the valves 40 and 42-will remain closed. As will be pointed outin greater detail hereinbelow, a decrease in the torque on outputfmember78 will allow spring 75 to rotate lug 67 into engagement with link 59 tomove pinch lever 52 clockwise to open valve 42 whereby the fluid motor20 is connected tothe sump 34 and the electrode 13 is lowered.Conversely, an

increase in the torque on output member 78 will rotate lug 67a intoengagement with link 59a to open valve,52a so that the fluid motor 20is'conn'ected to \the pressure source 30 and the electrode 13 is raised.7 1

The control circuit 27Ifor the electromagnetic clutch 72 includes afirst resistor 80 connected 'tothe electrode phase conductor 16 by meansof a'current transformer 82, a potentiometer 83 connected across thesecondary winding of the current transformer 82, and a full-waverectifier 84 so that a voltage is derived across resistor80 which isproportional to the current flowing in electrode 13. Control circuit 27also includes second resistor 86 connected to the phase conductor 16through a potentiometer 8 8 and a full-wave rectifier 89 so that avoltage is derived across resistor 86 which is proportional to thevoltage across the electrode 13. It can also be seen that the voltagesderived across resistors 80 and 86 are subtractive- In addition, controlcircuit 27 includes an adjustable bias resistor 90 which is connectedthrough a full-wave rectifier 92 to a source of alternating current 93in such a man ner that the voltages across resistors 80 and 90 areadditive.

It will be appreciated that the voltage derived across resistor 80. plusthat derived across resistor 90 minus that derived across resistor 86will be'the excitation voltage for coil-79 sothat the degree of couplingbetween clutch input member 76 and. clutch output member 77 will;- be afunction'of the algebraic sum of these voltages; Potentiometers .83 and88 and resistor 9t) are so adjusted that when the electrode current andvoltage conditions are correct the excitation applied to coil 79 willprovide sufficient coupling between the input member 76 andthe outputmember 78 to just hold the valve member 71 in a balanced conditionrelative to the spring 75 so that each of the valves 40 and 42 will beclosed and the electrode 13 will'be held in position. I

Should the'gap between electrode 13' and melt 12 become too'large,causing an increase in arc'voltage and a decrease injarc current, thevoltage across resistor 86 will increase and the voltage across resistor80 will'dcrease. As a result, the excitation in the coil 79 willdecrease below that required to'hold the valve member 71 in its neutralposition and it will be rotated counterclockwise through a slight angleby the spring 75un'til the spring 75 torque is equal to that exerted bythe clutch output member 78 and the spring 56, Suchcounterclockwiserotation of valvemember" 71'will movelug 67 intoengagement with' link 59'to rotate pinch rod 52 clockwise to open thevalve 42 thereby connecting the pressure side of piston'24 tothe sump 34which'allows'the electrode 13 to begin lowering. the electrode 13 lowersthe electrodevoltage will decrease and the electrode cur rent willincrease so that the excitation of coil 79 will also raise until iteisagain at the optimum of value, whereupon the output torque on valvemember 71 will match that exerted by the spring 75, whereupon merm ber'71 will again assume its neutral position "wherein valve 42 isC1osedand the electrode 13'isstationary. f Should the gap between electrode 13and-the furnace charge 12 become too short, causing an increase in arccurrent and a decrease in arc. voltage,the voltage ,acros's' resistor 80will increase'and that acrossresistor 86 will tatecountercldckwiseagainst springs 75 and 56a. and

decrease. Upon this event the excitation. -on coil79 will increase fromthe optimum-value, thereby increasingthe output torque'v on the valvemember 71"causing it torothereby .to open valve 40. This. connects thepressure side of pist0n24 to'the hydraulic accumulatorv30 whereuponhydraulic pressure will raise the electrode 13 As the electrode 13rises,.the' arc'voltage will increase and the arc'currentwill decreasewhereby the excitation of .coil 79 will also decrease toward the optimumvalue so that when electrode current, and voltage conditions are againin balance valve member 71 will have returned to its neutral positionwherein the .valve 40 is closed and electrode 13 is stationary. 1

It will beappreciated that the rate offluid flow through the valves 40and 42.will vary fromsome zero value when their respective pinch levers52 and 52a. are in their fully closed positions to some maximum .valueswhen these levers are in their fully rotated positions; Since the .de-

' g'ree that each pinch lever rotates from its closed position hydraulicmotor 20, without the necessity of pilot valves and control valves tosense and amplify electrode voltage and current changes. v fl s In orderto permit manual operation during the beginning or end of eachoperation, solenoid operated valves 1% and 101 may be provided in bypassconduits 102 and 103, respectively, which are in turn respective-1yconnected in parallel with pinch valves 40 and 42.

FIG. 4'shows an alternate embodiment of the invention, wherein asecond-electromagnetic clutch assembly 72 is provided for driving thevalve member 71- in an electrode'lowering direction. This provides abalanced system and eliminates the necessity for a biasing Spring 75.The second electromagnetic clutch 72' is identical with theelectromagnetic clutch 72 and, accordingly, corresponding parts havebeen given the same reference numeral. except that each is distinguishedby a prime in the former.

' The electromagnetic clutch 72 of FIG. 4'is operative to impart acounterclockwise torque on the valve member 71 for opening the pinchvalve 40 to initiate an electrode raising operation. Toward this end,the coil 79 of clutch 72 is connected to resistor 80, so that the coil79- will receive an exciting voltage proportional to the current inelectrode 13. On the other hand, the clutch 72' is operative to impart aclockwise torque on the valve member 71 to open pinch valve 42 andinitiate an electrode lowering operation. For this reason the coil 79 ofclutch 72' is connected to resistor 80' so that it will receive anexcitation voltage proportional to the voltage in electrode -13. It isalso desirable in the embodiment of'FIG. 4 to .provide a first biasingpotentiometer 90 in series with resistor 80 and a second biasingpotentiometer 90 in series with the resistor 80. The biasingpotentiometers 90 and 90 are each connected to a source 93 through arectifier 92 in such amanner that the voltage drop across each is inopposition to its respective series connected resistor 80 and 80, sothat these voltages will be subtractive from .the voltages inducedacross said resistors.

When voltage and current conditions in electrode 13 are in balance,there will be zero torque on valve output member71 as the outputs ofeach of the clutches 72 and 72' will be equal and opposite acting;Should the arc gapbecome too short, causing an increase in arc currentand a decrease in arc voltage, the output of clutch 72 will increase,and the output of clutch 72 will decrease, causing a netcounterclockwise torque on output member 71 to open valve 40 andinitiate an electrode raising operation. Should the arc gap become toolong, on the other hand, causing an increase in arc voltage and adecrease in arc current, the output torque from clutch 72' will increaseand the output of clutch 72 will decrease, to cause a netcounterclockwise torque on valve member 71, so

that valve 42 will open to initiate an electrode lowering operation.

Because identical clutch and motor arrangements are employed forimparting both clockwise and counterclockwise torques to the valvemember 71, a balanced system is obtained and equal torques are employedfor opening each of the pinch. valves 40 and 42 in contrast to theembodiment of FIG. 1, on the other hand, where a spring 75 is employedto impart clockwise torque to the valve member 71.

While only two embodiments of the invention have ,been shown anddescribed, and while they have been illustrated with respect to one typeof hydraulic system, it is intended that the invention be limited onlyby the scope of the appended claims.

I claim:

1. In an electric arc furnace, the combination of a ,furnace body and anelectrode, a hydraulic motor connected to said electrode, a hydraulicpressure system,

valve means operable in one manner to connect said hydraulic motor tosaid pressure system in an electrode raising relation and in anothermanner to connect said hydraulic motor to said pressure system in anelectrode lowering relation, continuously operable electric motor means,electromagnetic clutch means coupled to said 'electric motor means andoperatively associated with said -valve means, a first electrical signalsource coupled to said electrode-for producing a first signalfunctionally related to the current in said electrode, said first signalsource also being connected to said clutch means for opcrating saidvalve means in said one manner so that said electrode will be raisedWhen the current therein rises above a desired value, and a secondelectrical signal 1 source coupled to said electrode for producing asecond signal functionally related to the voltage in said electrode,said second signal means also being connected 'to said clutch means foroperating said valve means in said another manner so that said electrodewill be lowered when its voltage rises above a desired value.

2. In an electric arc furnace, the combination of a furnace body and anelectrode, a hy raulic motor connected to said electrode, a hydraulicpressure system,

valve means operable in one direction to connect said hydraulic motor tosaid pressure system in' a manner tending to raise said electrode and inanother direction -to connect said hydraulic motor to said pressuresystem in a manner tending to lower said elect-rode, continuously'operable electric motor means, electromagnetic clutch means havingmagnetic input means coupled to said electric motor means and magneticoutput means operatively associated with said valve means, said clutchmeans including exciting coil means for producing coupling between saidinput and output means to move said output means in accordance with themagnitude and sense of an applied electrical signal, a first electricalsignal source coupled to said electrode for producing a first signalfunctionally related to the current in said electrode, said first signalsource also being connected to said coil means in a sense tending tomove said output means in said one direction so that said electrode willbe raised when the current therein rises abovea desired value, and asecond electrical signal source coupled to said electrode for producinga second signal functionally related to the voltage in said electrode,said second signal means also being connected to said coil means in asense tending to move said output means in said another direction sothat said electrode will be lowered when its a desired value.

3. In an electric arc furnace, the combination'of a voltage rises above-furnace body, an electrode, a hydraulic motor connected to saidelectrode, a hydraulic pressure system, first nor mally closed pinchvalve means operable in one direction to connect said hydraulic motor tosaid pressure'system motor means for operating said valves in saidanother direction, a first electrical signal source coupled to saidelectrode for producing a first signal functionally related to thecurrent in said electrode and connected to said electroresponsive meansin a sense tending to increase the coupling between said motor and eachof said valve means, and a second electrical signal source coupled tosaid electrode for producing a second electric sign-a1 functionallyrelated to the voltage in said electrode and con- .nected to saidelectroresponsive means in a sense tending to decrease the couplingbetween said electric motor means and each of said valve means.

4. In an electric arc furnace, the combination of a furnace body and anelectrode, a hydraulic motor connected to said electrode, a hydraulicpressure system, valve means operable in one direction to connect saidhydraulic motor to said pressure system in a manner tending to raisesaid electrode and in another direction to .connect said hydraulic motorto said pressure system in a manner tending to lower sai-d electrode,continuously operable electric motor means, electromagnetic clutch meanshaving magnetic input means coupled to said motor and magnetic outputmeans operatively associated with said valve means, said electric motormeans opersaid electrode will be raised when the current therein risesabove a desired value, and a second electrical signal source coupled tosaid electrode for producing a second voltage signal functionallyrelated to the voltage in said electrode,

, said second signal means also being connected to said coil means in asense tending to decrease the coupling between said input and outputmeans so that said electrode will be lowered when its voltage risesabove a desired value.

5. In an electric arc furnace, the combination of a furnace body and anelectrode, a hydraulic motor connected to said electrode, a hydraulicpressure system, first and second pinch valve means each having variableflow restricting means and control means, a first one of said controlmeans being operable in a first direction to move a vfirst one of saidflow restricting means between closed and controlled open positions toconnect said hydraulic motor to said pressuresystem in a manner tendingto raise said electrode, the second one of said control means being,operable in another direction to move the second one of said flowrestricting means between closed and controlled open positions toconnect said hydraulic motor to said pressure system in a manner tendingto lower said electrode, continuously operable electric motor means,electromagnetic' clutch means having an exciting coil, saidclutch meansalso having input means coupled to said electric motor means and outputmeans operatively associated with said'control means for selectivelyoperating the latter 1 in accordance with the magnitude of an appliedelectrical signal, said electric motor means tending to operate saidoutput means in said one direction, means biasing said output means insaid another direction, a first electrical signal source coupled to saidelectrode for producing a first voltage signal functionally related tothe current in said electrode, said first signal source also beingconnected to said coil means in a sense tending to increase the couplingbe tween said input and output means so that said electrode will beraised when the current therein rises above a desired value and a secondelectrical signal source coupled to said electrode for producing asecond voltage, signal functionally related to the voltage in saidelectrode, said second signal means also being connected to said coilmeans in a sense tending to decrease the coupling beitween said inputand output means so that said electrode will be lowered when its voltagerises above a desired value.

6. In an electric arc furnace, the combination of a "furnace body and anelectrode, a hydraulic motor, a hytdraulic pressure system, valve meansoperable in one direction to connect said hydraulic motor to saidpressure system 1n a manner tending to raise said electrode and inanother direction to connect said hydraulic motor to said pressuresystem in a manner tending to lower said electrode, continuouslyoperable electric motor means, elec- :tromagnetic clutch means havingmagnetic input means coupled to said electric motor means and magneticoutput means operatively associated with said valve means,

said electric motor means operatingsaid input means in said onedirection, means biasing said output means in said another direction,said clutch means including exciting coil means for producing couplingbetween said input and output means in accordance with the magnitude ofan applied electrical signal, a first electrical signal source coupledto said coil in a sense tending to produce coupling between said inputand output means in opposition to said biasing means, a secondelectrical signal source coupled to said electrode for producing asecond signal functionally related to the current in said electrode,said second signal source also being connected to said coil means in anadditive sense relative to said first signal source to move said outputmeans in said first direction whereby said electrode will be raised whenthe current 'therein rises above a desired value, and third electricalsignal source coupled to said electrode for producing a third signalfunctionally related to the voltage in said electrode, said third signalmeans also being connected to said coil means in a subtractive senserelative to said first signal source so that said biasing means can movesaid output means in said another direction whereby said electrode willbe lowered when its voltage rises above a desired value. 7

7. The combination set forth in claim 6 wherein said valve meanscomprises first variable flow pinch valve means operable in onedirection to connect said hydraulic motor to said pressure system in amanner tending, to

raise said electrode and second variable flow pinch valve means operablein another'direction to connect said hydraulic motor to said pressuresystem in a manner tending to lower said electrode. 7

8. In an electric arc furnace, the combination of a furnace body, anelectrode, a hydraulic motor connected to said electrode, a hydraulicpressure system, first normally closed valve means operable in onedirection to connect said hydraulic motor to said pressure system in amanner tending to raise said electrode, second normally closed valvemeans operable in another direction to connect said hydraulic motor tosaid pressure system in a manner tending to lower said electrode,-firstand second continuously operable electric motor means, firstelectroresponsive variable transmission means operable to couple saidfirst electric motor means to said valves for operation in said onedirection in accordance with the magnitude of a first applied electricalsignal and second electroresponsive variable transmission means operableto couple said second electric motor means to said valves foroperationin an opposite direction in accordance with the magnitude of a secondapplied electrical signal, a first electrical signal source cou led tosaid electrode-for producing a first signal functionally related to thecurrent in said electrode and connected to said first electroresponsivemeans in a sense tending to increase coupling between said first motormeans and each of said valve means for operation in said one direction,and a second electrical signal source coupled to said electrode forproducing a second electric signal functionally related to the voltagein said electrode and connected to said electroresponsive means in asense tendring to increase the coupling between said'second motor meansand each of said valves for operation in said opposite direction.

9. The combination set forth in claim 8 wherein each of said normallyclosed valve means is a variable flow pinch valve.

10. In an electric arc furnace, the combination of a furnace body and anelectrode, a hydraulic motor, a hydraulic pressure system, valve meansoperable in one direction to connect said hydraulic motor to saidpressure system in a manner tending to raise said electrode and in anopposite direction to connect said hydraulic motor to said pressuresystem in a manner tending to lower said electrode, first and secondcontinuously operable electric motor means, first and secondelectromagnetic clutch means each having magnetic input means coupled toone of said electric motor means and magnetic output means coupled tosaid valve means, said first electric motor means operating said firstinput means in said one direction, said second electric motor meanoperating said second input means in an opposite direction, each of saidclutch means including exciting coil means for producing couplingbetween its respective input and output means in accordance with themagnitude of an applied voltage signal, a first electrical signal sourcecoupled to said electrode for producing a first signal functionallyrelated to the current in said electrode, said first signal source alsobeing connected to said first coil means in a sense tending to move saidvalve means in said first direction whereby said electrode will beraised when the current therein rises above a desired value, a secondelectrical signal source coupled to said electrode for producing asecond signal functionally related to the voltage in said electrode,said second signal means being connected to said second coil means in asense tending to move said valve means in said opposite directionwhereby said electrode will be lowered when its voltage rises above adesired value.

11. The combination set forth in claim wherein said valve meanscomprises first variable flow pinch valve means operable in onedirection to connect said hydraulic motor to said pressure system in amanner tending to raise said electrode and second variable flow pinchvalve means operable in another direction to connect said hydraulicmotor to said pressure system in a manner tending to lower saidelectrode.

12. In an electric arc furnace, the combination of a furnace body and anelectrode, a hydraulic motor connected to aid electrode, a hydraulicpressure system, valve means operable in one manner to couple saidhydraulic motor to said pressure system in an electrode raising relationand in another manner to couple said hydraulic motor to said pressuresystem in an electrode lowering relation, continuously operableelectromotive means, electroresponsive variable transmission means forcoupling said electromotive means to said valve means, a firstelectrical signal source coupled to said electrode for producing a firstelectrical signal functionally related to the current in said electrode,said first signal source also being connected to said electroresponsivevariable transmission means for coupling said valve means to saidelectromotive means for operating said valve means in said one manner sothat said electrode will be raised when the current therein deviatesfrom a desired value, and a second electrical signal source coupled tosaid electrode for producing a second signal functionally related to thevoltage in said electrode, said second signal means also being connectedto said electroresponsive variable transmission means for coupling saidvalve means to said electromotive means for operating said valve meansin said another manner so that said electrode will be lowered when itsvoltage deviates from a desired value.

13. In an electric arc furnace, the combination of a furnace body and anelectrode, a hydraulic motor connected to said electrode, a hydraulicpressure system, valve means operable in one direction to couple saidhydraulic motor to said pressure system in a manner tending to raisesaid electrode and in another direction to couple said hydraulic motorto said pressure system in a manner tending to lower said electrode,continuously operable electromotive means, electroresponsive variabletransmission means having input means coupled to said motive means andoutput mean operatively associated with said valve means, saidelectroresponsive variable transmission means includingelectroresponsive means for producing coupling between said input andoutput means to move said output means in accordance with the magnitudeand sense of an applied electrical signal, a first electrical signalsource coupled to said electrode for producing a first signalfunctionally related to the current in said electrode, said first signalsource also being connected to said electroresponsive means in the sensetending to move said output means in said one direction so that saidelectrode will be raised when the current therein rises above a desiredvalue, and the second electrical signal source coupled to said electrodefor producing a second signal functionally related to the voltage insaid electrode, said second signal means also being connected to saidelectroresponsive means in a sense tending to move said output means insaid another direction so that said electrode will be lowered when itsvoltage rises above a desired value.

References Cited by the Examiner UNITED STATES PATENTS 412,013 10/1889Beebe 2519 2,450,427 10/1948 Hal-pert 91459 FOREIGN PATENTS 524,9895/1956 Canada.

JOSEPH V. TRUHE, Primary Examiner.

1. IN AN ELECTRIC ARC FURNACE, THE COMBINATION OF A FURNACE BODY AND ANELECTRODE, A HYDRAULIC MOTOR CONNECTED TO SAID ELECTRODE, A HYDRAULICPRESSURE SYSTEM, VALVE MEANS OPERABLE IN ONE MANNER TO CONNECT SAIDHYDRAULIC MOTOR TO SAID PRESSURE SYSTEM IN AN ELECTRODE RAISING RELATIONAND IN ANOTHER MANNER TO CONNECT SAID HYDRAULIC MOTOR TO SAID PRESSURESYSTEM IN AN ELECTRODE LOWERING RELATION, CONTINUOUSLY OPERABLE ELECTRICMOTOR MEANS, ELECTROMAGNETIC CLUTCH MEANS COUPLED TO SAID ELECTRIC MOTORMEANS AND OPERATIVELY ASSOCIATED WITH SAID VALVE MEANS, A FIRSTELECTRICAL SIGNAL SOURCE COUPLED TO SAID ELECTRODE FOR PRODUCING A FIRSTSIGNAL FUNCTIONALLY RELATED TO THE CURRENT IN SAID ELECTRODE, SAID FIRSTSIGNAL SOURCE ALSO BEING CONNECTED TO SAID CLUTCH MEANS FOR OPERATINGSAID VALVE MEANS IN SAID ONE MANNER SO THAT SAID ELECTRODE WILL BERAISED WHEN THE CURRENT THEREIN RISES ABOVE A DESIRED VALUE, AND ASECOND ELECTRICAL SIGNAL SOURCE COUPLED TO SAID ELECTRODE FOR PRODUCINGA SECOND SIGNAL FUNCTIONALLY RELATED TO THE VOLTAGE IN SAID ELECTRODE,SAID SECOND SIGNAL MEANS ALSO BEING CONNECTED TO SAID CLUTCH MEANS FOROPERATING SAID VALVE MEANS IN SAID ANOTHER MANNER SO THAT SAID ELECTRODEWILL BE LOWERED WHEN ITS VOLTAGE RISES ABOVE A DESIRED VALUE.